The inner surface of a pneumatic tire may include an elastomeric composition designed to prevent or retard the permeation of air from the tire's inner air chamber. This elastomeric composition is often referred to as an innerliner. Rubbers, such as butyl and halobutyl rubber, which are relatively impermeable to air, are often used as the primary rubber component in innerliners.
The innerliner may comprise a relatively thin sheet of elastomer that is formulated with compounding additives and a curing system. The elastomer formulation may be laminated to the inner surface of a tire carcass layer of an uncured tire as the tire is formed on a tire building drum. Final cure of the composite structure produces a tire having a cured innerliner adhered to the carcass.
Properties that are desirable for innerliners include good resistance to air permeation, flex resistance, and adhesion to the tire carcass. Low permeability to air is generally achieved through the use of a high mechanical Tg polymer, such as butyl rubber or a halobutyl rubber. The high Tg polymer may be blended with other elastomers such as SBR or natural rubber. Flex resistance and tensile strength will depend, to some degree, on modulus.
Natural and butyl rubber may be vulcanized by using sulfur curative systems. Halobutyl rubber may be cured by using metal oxide curative systems and sulfur cure systems.
Typical amounts reported in the literature for halobutyl rubber or blends of halobutyl rubber with natural rubber are 3 to 5 parts per hundred rubber (phr) zinc oxide, and 0.5 to 1 phr sulfur.
Thus, a method would be desirable for preparing a tire innerliner formulation having a good combination of properties including air permeability, flex resistance, tensile strength elongation, and adhesion. Specifically desirable is a vulcanizable composition including one or more rubbery polymers and a cure system that results in an innerliner formulation with an optimum combination of these properties.